Radio Frequency (RF) receivers are ubiquitous in all aspects of modern communications systems (e.g., cellular, satellite, wireless networks, etc.). The zero-IF (Intermediate Frequency) is a design methodology which greatly simplifies the RF receiver compared with the traditional superheterodyne designs. In zero-IF receiver the RF signal is directly down-converted to baseband using a quadrature down-converter. The output of the quadrature down-converter are two in-phase/quadrature (I/Q) components; and it is crucial to have the quadrature components I/Q balanced so that no image signal is present in the baseband when the components are combined. In practice, designing a balanced quadrature down-converter can be challenging due to, e.g., device mismatches, non-ideal components, temperature effects, etc. A common approach to combat the imbalances has been to use quadrature compensators, which compensate for imbalances by applying phase, gain, DC corrections. However, these methods are not able to remove imbalances across the entire frequency bandwidth; accordingly, RF zero-IF receivers suffer from performance degradation.
Conventional zero-IF receiver designs have dealt with a single channel or a single carrier. These designs experience performance degradation due to quadrature imbalance, channel flatness and variation over the operating temperature. In some cases, the degradation due to the impairments is compensated on per carrier basis. A main drawback of this approach is that it is a single channel/carrier design. This, it has to be replicated many times to achieve multi-channel/carrier receiver. Also, it cannot be used as a frequency conversion device.
Therefore, there is a need to design enhanced zero-IF receivers in which imbalances in quadrature components are compensated for completely. Different embodiments address these deficiencies and others in the design of zero-IF receivers and result in significantly improved RF receivers with robust performance across a large frequency band in a variety of systems such as multi-channel and multi-carrier systems and across wide range of operational conditions (e.g., temperature variations).